The present invention relates to an optical pickup apparatus for reading information from an information recording medium and writing information onto the information recording medium with use of a laser light beam. More specifically, the present invention relates to a front monitor-type optical pickup apparatus, that is an optical pickup apparatus which emits a laser light beam to the information recording medium from a laser light source and detects quantity of the laser light so as to execute feedback control of the output power from the laser light source.
It is noted that typical examples of the information recording medium include DVD (Digital Video Disk) and CD (Compact Disk).
Further, the present invention relates to a manufacturing method for manufacturing such front monitor-type optical pickup apparatuses.
This kind of the front monitor-type optical pickup apparatus is basically composed of a diffraction grating 2, a reflection mirror 3, a beam splitter 4, a collimate lens 5 and an object lens 6 disposed along a route of a laser light beam emitted by a semiconductor laser 1 toward an information recording medium (optical disk) 8, and also provided with a front monitor detector 7 as shown in FIG. 1. The laser light beam emitted from the semiconductor laser 1 is radiated to the optical disk 8 through the diffraction grating 2, the beam splitter 4, the collimate lens 5 and the object lens 6. At the same time, part of the laser light beam is reflected by the reflection mirror 3 and comes into the front monitor detector 7, and the front monitor detector 7 detects quantity of the incident light beam. Then, an unshown feedback control system executes feedback control of the driving current supplied to the semiconductor laser 1 so as to keep the output level from the front monitor detector 7 constant, thereby keeping the output power from the semiconductor laser 1 at a constant rate (refer to Japanese Patent Laid-Open Publication No. 2000-21001 (Paragraph 0004-0008 on P2, FIG. 3)).
The above-mentioned front monitor detector 7 is housed in an unshown housing whose upper portion is opened. Conventionally, the inner size of the housing is set substantially equal to the size of the front monitor detector 7 (more properly including a flexible substrate with the front monitor detector 7 mounted thereon). In assembling an optical pickup apparatus, the front monitor detector 7 is inserted into the housing from the upward side. The front monitor detector 7 is fit into the housing, and secured in the position where the front monitor detector 7 is in contact with the bottom face of the housing. Thus, mounting accuracy of the front monitor detector 7 on the housing has been conventionally attempted to be increased by coinciding the inner size of the housing with the size of the front monitor detector 7.
In the front monitor-type optical pickup apparatus, due to component and assembly dispersion such as radiation characteristics dispersion of the semiconductor laser 1, reflectance and mounting dispersion of the reflection mirror 3, and mounting dispersion of the front monitor detector 7, there is generated dispersion in quantity of incident light upon the front monitor detector 7.
Influence of such dispersion in quantity of incident light to the front monitor detector 7 may be restrained in respective optical pickup apparatus by gain-adjusting the feedback control system with use of an external resistance. However, in the case of carrying out gain adjustment with use of an external resistance, a response speed of the feedback control system is influenced even if the output power of the semiconductor laser 1 is fallen within an appropriate range.
This influence becomes serious when write access to the optical disk 8 is performed, more specifically, when write access is performed to the optical disk 8 by a slim-type optical pickup apparatus (having narrow vertical width) such as one incorporated in a notebook computer.